The phenomenon in which listeners’ impressions of music are unintentionally altered even when the same sound source is played back remains an important issue. Previous research has shown that the state; combination of audio equipment affect the characteristics of nonlinear distortion in music playback. Hence, we conducted a subjective evaluation of auditory; musical impressions using sound sources with various nonlinear distortions. However, the subjective evaluation was unstable; difficult to assess. The reason was that the sound change was perceived emotionally as a slight change in sound image; musicality,; the interpretation of evaluation terms varies widely among subjects due to the difficulty of verbalizing the impression. Therefore, we evaluated the change in listeners’ stress caused by nonlinear distortion in music playback using the photoplethysmography (PPG). In this study, we conducted a follow-up experiment with improved accuracy. In the experiment, 41 subjects listened to sound sources with even-order harmonic distortion at 2.69% THD, odd-order harmonic distortion at 2.69% THD,; no distortion. The musical piece of sound sources is an original to eliminate familiarity; bias toward existing music. We evaluated changes in subjects’ stress states using the mean pulse-pulse interval (PPI); the root mean square of successive differences (RMSSD), computed from the PPG signal, as indicators of stress. These results reconfirm that nonlinear distortion in music playback affects listeners’ vital responses, as evidenced by significant differences in both mean PPI; RMSSD, as assessed by Cochran's Q test at the 5% significance level.
